Senate Majority Leader Harry Reid gave a forceful defense of congressional earmarks on Tuesday, a sign that bipartisan legislation to permanently ban pork-barrel spending will have a tough road in the Senate.

“I’ve done earmarks all my career, and I’m happy I’ve done earmarks all my career. They’ve helped my state, and they’ve helped different projects around the country,” an unapologetic Reid told reporters after the Democrats’ weekly caucus lunch. He called senators’ right to direct spending to pet projects in their home states is a “constitutional duty.”

“And I repeat, I will not stand by and be driven down this path … that I think is taking away from what the Founding Fathers wanted, three separate but equal branches of government,” he added. “I don’t believe that the White House has the authority to tell me how I should spend money in Nevada.”

Sens. Claire McCaskill (D-Mo.) and Pat Toomey (R-Pa.) introduced the permanent earmark ban as an amendment to a popular insider trading bill, known as the STOCK Act, that’s now being debated on the Senate floor.

But Senate aides said Reid could block the amendment by holding a vote to end debate on the STOCK Act. At that point, only amendments germane to the underlying bill could be considered, and there’s general agreement the earmark ban is not relevant.

Shortly after the 2010 election, Senate Minority Leader Mitch McConnell (R-Ky.) fought a temporary ban on earmarking before eventually voting with conservatives in his conference to pass a nonbinding two-year moratorium that expires at the end of this year. Senate Appropriations Committee Chairman Daniel Inouye (D-Hawaii) soon followed suit, announcing that his panel would ban earmarks from any bills through 2012.

McConnell has not spoken publicly about whether he supports the proposed permanent ban, and aides said Tuesday they were unsure of his position.

Toomey, a tea party favorite and the former head of the conservative Club for Growth, said he hadn’t sought support from McConnell and other GOP leaders but remains “cautiously optimistic.”

“Both sides of the aisle adopted a temporary moratorium, thereby demonstrating their acknowledgment that we ought not to be earmarking,” Toomey told POLITICO. “A legislative ban that is solid ought to be able to enjoy enough support to be passed.”

During a colloquy with Toomey on the Senate floor, McCaskill said a permanent ban is needed to stop senators “who want to go back to the old ways.”

“For too long, too many senators believed the measure of their worth as a senator had to do with how much money they were bringing home,” she said. A senator’s worth “should be based on how much money you can save.”